CVD apparatus

ABSTRACT

An improved CVD apparatus for depositing a uniform film is shown. The apparatus comprises a reaction chamber, a substrate holder and a plurality of light sources for photo CVD or a pair of electrodes for plasma CVD. The substrate holder is a cylindrical cart which is encircled by the light sources, and which is rotated around its axis by a driving device. With this configuration, the substrates mounted on the cart and the surroundings can be energized by light of plasma evenly throughout the surfaces to be coated.

RELATED APPLICATIONS

This application is a Division of application Ser. No. 09/188,382, filedNov. 10, 1998, now U.S. Pat. No. 6,013,338; which itself is a Divisionof application Ser. No. 08/769,115, filed Dec. 18, 1996 (now U.S. Pat.No. 5,855,970); which is a Divisional of application Ser. No.08/376,736, filed Jan. 23, 1995, (now U.S. Pat. No. 5,629,245); which isa Division of application Ser. No. 07/971,242, filed Sep. 8, 1992 (nowU.S. Pat. No. 5,427,824); which is a Continuation of application Ser.No. 07/702,492, filed May 20, 1991, now abandoned; which is aContinuation-In-Part of application Ser. No. 07/497,794, filed Mar. 22,1990, now abandoned; which is a Continuation of Ser. No. 07/091,770,filed Sep. 1, 1987, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to a photo enhanced CVD apparatus.

Many chemical vapor deposition (CVD) processes are used, such as APCVD,LP CVD, plasma CVD, thermal CVD and so forth, for depositing a film on asubstrate. While these processes have their own peculiar characteristicsrespectively, the temperature at which each process is carried out iscommonly rather high. Such high temperature process is not suitable forformation of passivation film on an aluminum electrode arrangement.

Photo enhanced CVD process has attracted the interest of artisansbecause it can be carried out at a comparatively low temperature. Thisprocess is based on the energy of light, namely an optical reaction iscarried out. For example, in the case of photo CVD process using silaneand ammonia, mercury atoms are excited by irradiation of ultravioletlight of 2,537 Å in wavelength. The process is carried out to deposit asilicon nitride film on a substrate in accordance with the followingequation:

 Hg+h--->Hg*(“*” is a symbol for excitation)

Hg*+SiH₄--->SiH₃+H−+Hg(“−” is a symbol for radical)

Hg*+NH₃--->NH₂—+H−+Hg

yNH₂ —+xSiH₃--->Si_(x)N_(y)+zH₂

In the above equations, x, y and z are chosen appropriately.

FIG. 1 is a cross-section view showing a photo CVD apparatus which hasbeen devised by the inventors in advance of the present invention. Tofacilitate the understanding of the background of the present invention,this apparatus will be briefly explained. In the figure, the apparatuscomprises a reaction chamber 31, light source chambers 39 andultraviolet light sources 41. Between the light source chambers 39, acart 35 is mounted so as to be capable of moving in the directionperpendicular to the drawing sheet. The cart is provided with heaters 37to heat substrates mounted on the external surfaces of the cart 35facing to the light source chambers 39. The temperature of thesubstrates 33 is elevated to about 200° C. which is suitable for forminga silicon nitride film. In the reaction chamber 31 is circulated aprocess gas at a pressure of several Torrs. The process gas isirradiated through quartz windows 47 with light radiated from the lightsource 41. A numeral 45 designates electrodes by virtue of whichdischarge takes place with the cart as the other electrode and undesiredproduct deposited on the surface of the quartz windows 47 can beeliminated by sputtering.

However, with this apparatus, the thickness of deposited film depends onth spatial relationship between the light sources and the position ofthe substrates. Namely, the product of the CVD process may be depositedwith a greater thickness at the position irradiated with stronger light.Generally speaking, the tolerable fluctuation of the thickness of thefilm is about 10%. Furthermore, the quartz windows 47 have to be thickto bear the differential pressure between the inside of the reactionchamber 31 and the light source chamber 39 in which cooling gas iscirculated. The differential pressure may cause leakage of the coolinggas from the light source chamber 39 into the reaction chamber 31. As analternative, a particular cooling system may be provided for the lightsource chamber so the pressure in the light source chamber, andtherefore the differential pressure, can be decreased. Also, whendischarge between the cart 35 and the reaction chamber 31 is desired toremove unnecessary film deposited on the light window by sputtering, thedischarge tends to deviate from the window. Because of this, theparticular electrodes 45 have to be provided which makes the size of theapparatus large.

As to unevenness of film deposited by CVD, it is also the problem in thecase of plasma CVD. The energy of plasma seems dependent on therelationship between the substrate and a pair of electrodes fordischarge. So a uniform deposition condition on a substrate to be coatedis also demanded for plasma CVD.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an CVD apparatuswith which a film can be deposited with a uniform thickness.

It is another object of the invention to provide a CVD apparatus withwhich a film can be deposited with high quality.

It is a further object of the invention to provide a cheaper CVDapparatus.

It is still a further object of the invention to provide a compact CVDapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section view of an example of a photo CVD apparatus.

FIG. 2 is a cross-section view showing an embodiment of the invention.

FIG. 3 is a cross-section view taken along a III—III line of FIG. 2.

FIG. 4 is a cross-section view showing another embodiment of theinvention.

FIGS. 5(A) to 5(C) are graphical diagrams showing the distributions ofthe intensity on substrates mounted on prism-shaped substrate holderhaving cross-sections of regular polygons of 6, 12, and 24 sides.

FIGS. 6(A) to 6(C) and FIG. 7 are section views showing the process ofan example of CVD in accordance with this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 2 and FIG. 3, a photo enhanced CVD apparatus inaccordance with the invention is illustrated. In the figure, theapparatus 1 comprises a reaction chamber 3, a hexagonal cart as asubstrate holder having six lateral faces on which substrates 15 aremounted, a driving device 9 with a motor 21 for rotating the cart 7around its axis, a plurality of quartz tubes 17, which may bealternatingly provided of different diameters, on the inside of thereaction chamber 3, with one end of each tube at a constant angulardistance around the cart 7 and with the other end of each tube beingclosed, mercury lamps 19 provided in and housed air-tightly by thequartz tube respectively, halogen lamp heaters 23 arranged along theaxial direction, a process gas introduction system 11, and an exhaustionsystem 13. A cooling gas, such as nitrogen gas, is circulated in thequartz tubes 17 by means of recirculation means 29. On each face of thecart 7, two substrates each 35 cm long and 30 cm wide can be mounted,and therefore the cart 7 can hold twelve substrates thereon. The cart ispreferentially removable from the driving device so that substrates canbe mounted outside the reaction chamber 3.

Next, the process in the apparatus will be explained. First, twelvesubstrates are mounted on the cart 7 and entered into the reactionchamber 3. After evacuating the reaction chamber 3 to 10⁻²-10⁻⁶ Torr bymeans of the exhaustion system 13, a process gas is inputted from theintroduction system 11 at about 3 Torr. Simultaneously, the substrates15 are heated by the heater 23 to about 200° C. Then, the cart 7encircled by the mercury lamps 19 is rotated at 2 rpm by the drivingdevice 9 and irradiated with ultraviolet light from the lamps 19,whereupon the product of a reaction initiated by optical energy isdeposited on the substrates 15. The product undesirably deposited on thequartz tubes 17 can be removed by sputtering in virtue of dischargebetween the cart 7 and the reaction chamber 3. Photo enhanced CVDprocess is carried out, e.g., in accordance with the following equation:

3Si₂H₆+8NH₃-->2Si₃N₄+21H₂

or

SiH₄+4N₂O-->SiO₂+4N₂+2H₂O  (1)

Referring now to FIG. 4, another embodiment of the invention isillustrated. This embodiment is same as the preceding embodiment exceptfor the number of side faces of a cart and provision of an electrode 49in the form of a cylindrical wire net disposed between the cart 7 andthe reaction chamber 3. The cart has twelve side faces each capable ofholding two substrates. The electrode 49 is used both for generatingplasma gas by discharging between itself and the cart 7, and forcarrying our etching eliminating unnecessary product deposited on theinside wall of the reaction chamber 3, the external surfaces of thelight sources 5 and so forth. The electrode 49 can be placed between thelight sources 5 and the cart 7 instead. Plasma CVD may be implementedsimultaneously by causing discharge during photo CVD process, or may beimplemented after deposition by photo CVD. Plasma CVD is carried out,e.g., using TEOS (tetra-ethyl-oxy-silane) in accordance with thefollowing equations:

SiO₄(C₂H₅)₄+140₂-->SiO₂+8CO₂+10H₂O,

or

SiO₄(C₂H₅)₄+28N₂O-->SiO₂8CO₂+10H₂O+28N₂  (2)

After taking out, from the reaction chamber, the substrates on which thedeposition has been deposited, undesirable deposited product is removedfrom the inside of the reaction chamber by means of etching in virtue ofdischarge between the cart 7 and the electrode 49. The etching iscarried out, e.g., in accordance with the following equations:

Si₃N₄+4NF₃-->3SiF₄+4N₂

3SiO₂+4NF₃→3SiF₄+2N₂+3O₂

To investigate the relationship between the uniformity of theillumination intensity on the substrate and the number of side faces ofthe cart, experimental data has been gathered. FIGS. 5(A) to 5(C) aregraphical diagrams showing the distributions of the intensity onsubstrates mounted on prism-shaped substrate holders havingcross-sections of regular polygons of 6, 12 and 24 sides. In the figure,the abscissa is the distance of the measuring point from the center of asubstrate, and the ordinate is the intensity normalized with referenceto the maximum intensity measured on the substrate. As shown from thediagrams, the distribution of the intensity becomes more uniform as thenumber of the faces increases. Namely, the intensity fluctuates over theirradiated surface at larger than 10% in the case of the cart having sixfaces, while the fluctuation of the intensity is limited within 5% inthe cases of the carts having twelve and twenty-four faces. The carthaving twenty-four faces may hold forty-eight substrate by mounting twosubstrates on each face.

FIGS. 6(A) to 6(C) are cross-section views showing an example of CVDprocess in accordance with the present invention. The surface of asubstrate to be coated is provided with a plurality of aluminum leadlines 51. The leads 51 are elongated in the direction perpendicular tothe drawing sheet with 0.8 micron in. height, 0.6 micron in width and0.9 micron in interval as shown in FIG. 6(A). A silicon oxide film isdeposited on the substrate over the leads 51 by photo CVD in accordancewith the equation (1) to the thickness of 0.3 to 0.5 at about 400° C. asshown in FIG. 6(B). Further, another silicon oxide film 55 is depositedby plasma CVD in accordance with the equation (2) at 200° C. as shown inFIG. 6(C).

The use of TEOS is advantageous particularly for forming a film on anuneven surface, specifically, it is possible to form a substantiallyeven or uniform film, even on a side surface of or on a lower surfacebetween the steps shown in FIG. 6(A) by reference numeral 51. It ispresumed that this is because TEOS is in a liquid state at roomtemperature and has a relatively large viscosity even when it isgasified. The even upper surface is desirable when provided with anoverlying aluminum electrode 57 as shown in FIG. 7. The likelihood ofdisconnection of electrode 57 is reduced by the even surface. After thecompletion of the deposition, the inside of the reaction chamber on themercury lamp 19, only one being schematically shown in FIGS. 6(A) to6(C). The etching process can be implemented on the deposited filmbefore or after plasma CVD in order to obtain even surface of the filmor to chamfer the edge of the film deposited.

By use of this process, film is deposited with a constant thicknessthroughout the surface of the substrate 15 in the light of the uniformirradiation over each substrate. However, the uniformity of thethickness can be further improved by modulating the intensity of themercury lamps 19 in synchronization with the rotation of the cart 7, orby modulating the angular speed of the cart 7 in correspondence with therelative position to the mercury lamps 19. According to the gist of theinvention, it is easily understood that the performance of non-photoenhanced plasma CVD is also improved by the use of the rotatablesubstrate holder.

The invention should not limited to the above particular embodiments andmodifications and variations are possible as would be recognized bythose skilled in the art. As the cross-section of the cart 7, otherregular or irregular polygons, or circle can be employed. Also thedriving device can be provided on the top side of the reaction chamber,or on the lateral side with pinion gear, in place of the bottom side asshown in FIG. 2.

What is claimed is:
 1. A method of forming a device comprising the stepsof: forming a first layer comprising silicon oxide over a substrateusing a first reactive gas containing at least one of monosilane anddisilane; forming a second layer comprising silicon oxide over saidfirst layer by plasma CVD using a second reactive gas comprisingtetra-ethyl-oxy-silane and an oxide gas; and cleaning an inside of achamber in which said second layer has been formed, wherein the cleaningstep is performed by using an etching gas containing fluorine.
 2. Amethod according to claim 1 wherein said oxide gas is selected from thegroup consisting of oxygen and nitrogen oxide.
 3. A method according toclaim 2 wherein said nitrogen oxide is N₂O.
 4. A method according toclaim 1, wherein the cleaning of said inside chamber is conducted inaccordance with a reaction, 3SiO₂+4NF₃→3SiF₄+2N₂+3O₂.
 5. A method offorming a device comprising the steps of: forming a first layercomprising silicon oxide over a substrate using a first reactive gascontaining at least one of monosilane and disilane; forming a layercomprising silicon oxide over said first layer by plasma CVD using asecond reactive gas comprising tetra-ethyl-oxy-silane and an oxide gas;and cleaning an inside of a chamber in which said second layer has beenformed, wherein the cleaning step is performed by using an etching gascontaining fluoride.
 6. A method according to claim 5 wherein said oxidegas is selected from the group consisting of oxygen and nitrogen oxide.7. A method according to claim 6 wherein said nitrogen oxide is N₂O. 8.A method according to claim 5 wherein the cleaning of said insidechamber is conducted in accordance with a reaction,3SiO₂+4NF₃→3SiF₄+2N₂+3O₂.
 9. A method of forming a device comprising thesteps of: forming a first layer comprising silicon oxide over asubstrate using a first reactive gas containing at least one ofmonosilane and disilane; forming a second layer comprising silicon oxideover said first layer by plasma CVD using a second reactive gascomprising tetra-ethyl-oxy-silane; and cleaning an inside of a reactionchamber in which said second layer has been formed, wherein the cleaningstep is carried out by using an etching gas comprising nitrogenfluoride.
 10. A method according to claim 9 wherein the cleaning of saidinside chamber is conducted in accordance with a reaction,3SiO₂+4NF₃→3SiF₄+2N₂+3O₂.
 11. A method of forming a device comprisingthe steps of: forming a first layer comprising silicon oxide over asubstrate using a first reactive gas containing at least one ofmonosilane and disilane; forming a second layer comprising silicon oxideover said first layer by plasma CVD using a second reactive gascomprising tetra-ethyl-oxy-silane and nitrogen oxide in accordance withthe following equation, Si(OC₂H₅)₄+24N₂O Si O2+8CO₂+10H₂O+24N₂; andcleaning an inside of a reaction chamber in which said second layer hasbeen formed, wherein the cleaning step is performed by using an etchinggas comprising nitrogen fluoride.
 12. A method according to claim 11wherein the cleaning of said inside chamber is conducted in accordancewith a reaction, 3SiO₂+4NF₃→3SiF₄+2N₂+3O₂.
 13. A method of forming adevice comprising the steps of: forming a first conductive layer over asubstrate; forming a first layer comprising silicon oxide over saidfirst conductive layer using a first reactive gas containing at leastone of monosilane and disilane; forming a second layer comprisingsilicon oxide over said first layer by plasma CVD using a secondreactive gas comprising tetra-ethyl-oxy-silane and an oxide gas;cleaning an inside of a reaction chamber in which said second layer hasbeen formed; and forming a second conductive layer over said secondlayer, wherein the cleaning step is performed by using an etching gascomprising nitrogen fluoride.
 14. The method of claim 13 wherein saidoxide gas is selected from the group consisting of oxygen and nitrogenoxide.
 15. The method of claim 14 wherein said nitrogen oxide is N₂O.